Method of determining columbium in iron and steel



Patented Sept. 27, 1949 UNITED STATES PATENT tim METHOD OF DETERMINING GOLUDIBIUM IN IRON AND STEEL James W. Hilliard, Cleveland, Ohio, ass'ignor to The American Steel and Wire Company of New Jersey, a corporation of New Jersey No Drawing. Application May 14, 194-5, I

Serial No. 593,772 7 6Claims. (01.235230? This invention relates to an improved method for the determination of columbium qualitatively and quantitatively in iron, steel, and various alloys thereof.

The invention has among its objects the provision of a quick, accurate, easily performed method of determining quantitatively the columbium content .in iron and steel, or various alloys thereof. v

The invention has as a further object the provision of an improved method of qualitatively determining columbium in iron and steel and various alloys thereof, characterized by the speed with which it may be carried out and the cheapness and simplicity of the apparatus employed.

The use of columbium in various iron and steel alloys, such as stainless steels toprevent intergranular corrosion, is becoming increasingly widespread. it is necessary in controlling production and fabrication of such alloys to make regular check analyses and one of the important tests is that for the presence of and amount of columbium. The test heretofore employedior the determination of'coiumb'ium has been unduly time-consuming and has necessitated the use of platinum ware in at least one part of the analysis, thereby adding greatly to the expense of making such analysis. In that method a test sample of the alloy was dissolved, columbium and silicon oxides were precipitated from the solution, the precipitate filtered, ignited, and the columbium and silicon oxides were weighed together. After this the ignited precipitate was placed in a platinum container and the silica was volatilized by the addition of hydrofluoric acid. The columbium oxide, then. free of silica, was reignited, reweighed,,-and[.the result employed in the computation of the amount of columbium present in the sample. This method involved the repetition of the steps of ignition and weighing, and did not allow the determination qualitatively of columbium until late in the analysis, that is, after the elimination of silica.

In the improved analytical method of myinvention the silica is eliminated as one of the first steps in the process, thereby allowing a qualitative determination of columbium to be made much earlier in the analysis. Furthermore, the silica is volatilized from the solution of the dissolved sample rather than from an ignited precipitate, so that the added hydrofluoric acid does not attack the ordinary glassware beaker employed to an extent great enough to affect the results. In addition, since the silica iseliminated from the solution, the precipitate of columbium oxide need be ignited and weighed but of the precipitate.

once in the quantitative determination of columbium. .As a result, a saving in time of as much as two hours over the former method is possible in each analysis by use of the method of the present invention. j

Briefly, the'improved method consists in adding sufficient hydrofluoric acid to the dissolved sample of the alloy to eliminate the silica, after which the solution is treated with perchloric acid to transpose the salts of all metals present in the sample, except chromium and columbium, to .perchlor-ates, the chromium to chromic acid and the columbium to columbium oxide. Since the latter is the only insoluble material present in the solution, the presence of a precipitate in the solution at this point indicates columbium in the sample. The columbium oxide and the solution are then conditioned for optimum filtering .The precipitate is ignited and weighed, after which'the amount of columbium present in the original sample may be calculated.

The following specific example of an analysis of a stainless steel for columbiumis typical of analyses in accordance with the present invention. It is to be understood, however, that the method may be employed with any iron or steel alloy, and that the quantities and concentrations of reagents used are capable of variation so long as they produce the statedresult.

Two grams of the sample were transferred to a 400 ml. covered beaker, .20 ml. of concentrated hydrochloric acid (specific gravity 1.19) and 5 ml. of nitric acid (specific gravity 1.42) were added and the solution was boiled gently until the sample was in solution. At this point all metals were in solution as chlorides and all carbides; with the exception of unpredictable amounts of molybdenumand columbium carbides, were broken down into the chlorides of their respective metals and into carbon dioxide. The silicon in the sample was then in the form of gelatinous silicic acid which was undissolved.

About 15 drops of hydrofluoric acid were then added to the solution int-he beaker while the beaker was swirled vigorously. Thereupon the silicic acid was eliminated from the solution by being volatilized assilicon tetrafluoride. All the columbium compounds present in the solution were converted to columbium fluoride. After the elimination of the silicon, 30. ml. of 5 perchloric acid was introduced, and the solution was rapidly evaporatedto dense fumes oi perchloric acid. The heating was continued until the perchloric acid condensed.down v the.,-sides'of the beaker.- Aftertheyfuming withperchloric acid, all-of the freehydrochloridnitric, and hydrofiuoric acids had been expelled from the solution, and all chlorides and fluorides, with the exception of chromium and columbium, had been transposed to soluble perchlorates. The chromium had been oxidized to chromic acid and the columbium fluoride had been changed to insoluble columbium oxide, the sole insoluble material in the solution. All remaining traces of carbides of metals in the solution had likewise been transposed as above. The beaker and its contents were then allowed to cool for approximately two minutes, 25 ml. of water was added, and the solution was heated to boiling for one or two minutes to expel free chlorine.

It is at this point in the analysis that the presence of columbium in the originalsample may be detected qualitatively. An amount of columhim, as low as .02% of the sample, may be detected by the presence in the solution at this point of a turbid cloud very readily distinguishable from the crystal clear solution resulting from a sample taken through the same steps but not containing columbium.

Since, in this particular instance, the presence of the insoluble chromiumoxide in the solution proved that the sample had contained columbium, the solution and the precipitate 'were conditioned for optimum filtration. 150 ml. of boiling water was added to the solution followed by 50 ml. of sulphurous acid, 10 ml. of concentrated hydrochloric acid (specific gravity 1.19) and one wafer of filtration accelerator, which is composed of pure cellulose. After the wafer had been thoroughly .macerated, the solution was boiled for five minutes. The solution was then digested on a steam plate until clear and then filtered through a close paper with the aid of a gentle suction, the beaker and precipitator being washed about ten times with hot 2% hydrochloric acid. The paper and precipitator were then transferred to a porcelain crucible, charred in an incinerator, and finally ignited at from. 1050 to 1100 C. After being cooled in a desiccator, the ignited precipitate, which consisted of pure columbium oxide, was then weighed. The percentage of columbium in the two gram sample was determined by multiplying the weight of the columbium oxide by 35. Where samples of different weights are employed, such percentage may.

be determined by the general formula:

Wt. Cb 05 X .70 X 100 Having thus fully disclosed my novel method of determining columbium, both quantitatively and qualitatively, in iron and steel and various alloys thereof, and having disclosed a typical manner in which such analytical methodmay be carried out, I desire to claim as new the following.

I claim:

1. The method of determining the presence of columbium in ferrous alloys which comprises first dissolving a sample of the alloy in a mixture of hydrochloric and nitric acids, next adding a sufficient amount of hydrofluoric acid to volatilizethe silicon as a fluoride of silicon, then addingperchloric acid to the resulting silicon-free solution, heating the solution in a vessel to evaporate it to dense fumes of perchloric acid, continuing the heating until perchloric acid condenses down the sides of the vessel, adding water to the solution and boiling it to expel freexchlorine, whereupon the presence of columbium in amounts of .02%

4 and over is revealed by the presence of a turbid cloud of columbium oxide in the solution.

2. The method of determining the presence of columbium in ferrous alloys which comprises first dissolving a sample of the alloy in a mixture of concentrated hydrochloric and nitric acids, approximately 10 ml. of hydrochloric acid and 2.5 ml. of nitric acid being employed for each gram of sample, next adding approximately 7.5 drops of hydrofluoric acid per gram of sample to volatilize the silicon as a fluoride of silicon, then adding approximately 15 ml. of 60% .perchloric acid per gram of sample to the resulting silicon-free solution, heating the solution in a vessel to evaporate it to dense fumes of perchloric acid, continuing the heating until perchloric acid condenses down the sides of the vessel, cooling the solution, adding water thereto, and boiling the solution to expel free chlorine, whereupon the presence of columbium in amounts of .02% and over is revealed by the presence of a turbid cloud of columbium oxide in the solution.

3. The method of determining columbium qualitatively and quantitatively in ferrous alloys which comprises first dissolving a sample of the alloy in a mixture of concentrated hydrochloric and nitric acids, next adding a sufficient amount of hydrofluoric acid to volatilize the silicon as a fluoride of silicon, then adding perchloric acid to the resulting silicon-free solution, heating the solution in a vessel to evaporate it to dense fumes of perchloric acid, continuing the heating until perchloric acid condenses down the sides of the vessel, adding water to the solution and boiling it to expel free chlorine, whereupon the presence of columbium in amounts of .02% and over is revealed by the presence of a turbid cloud of columbium oxide in the solution, then adding a substantial quantity of boiling water and a mixture of sulphurous and hydrochloric acids to the solution, then boiling and filtering the solution and finally igniting the resulting columbium oxide precipitate. V

4. The method of determining columbium qualitatively and quantitatively in ferrous alloys which comprises first dissolving a sample of the alloy in a mixture of approximately 10 ml. of concentrated hydrochloric acid and 2.5 ml. of concentrated nitric acid for each gram of sample, next adding approximately 7.5 drops of hydrofiuoric acid per gram of sample to volatilize the silicon as a fluoride of'silicon, then adding approximately 15 of 60% perchloric acid per gram of sample to the resulting silicon-free solution, heating the solution in a vessel to evaporate it to dense fumes of perchloric acid, continuing the heating until perchloric acid condenses down the sides of the vessel, coolingthe solution, adding water thereto and boiling it to expel free chlorine, whereupon the presence of columbium in amounts of .02% and over is revealed by the presence of a turbid cloud of columbium oxide in the solution, then adding a substantial quantity of boiling water and a mixture of sulphurous and hydrochloric acids to the solution, boiling and filtering the solution and finally igniting the resulting columbium oxide precipitate.

5. The method of determining columbium qualitatively and quantitatively in ferrous alloys which comprises first dissolving a sample of the alloy in a mixture of approximately 10 ml. of concentrated hydrochloric acid and 2.5 ml. of concentrated nitric acid for each gram'of sample,

next adding approximately 7.5 drops of hydrofluoric acid per gram of sample to volatilize the silicon as a fluoride of silicon, then adding approximately 15 ml. of 60% perchloric acid per' gram of sample to the resulting silicon-free solution, heating th solution in a vessel to evaporate it to dense fumes of perchloric acid, continuing the heating until perchloric acid condenses down the sides of the vessel, cooling the solution, adding water thereto, and boiling it to expel free chlorine, whereupon the presence of columbium in amounts of .02% and over is revealed by the presence of a turbid cloud of columbium oxide in the solution, then adding approximately 75 ml. of boiling water per gram of sample, 25 ml. of concentrated sulphurous acid 7 and 5 ml. of concentrated hydrochloric acid to the solution, then boiling the resulting solution for an appreciable time and filtering the solution, and finally igniting the thus precipitated columbium oxide.

6. The method of determining columbium qualitatively and quantitatively in ferrous alloys which comprises first dissolving a sample of the alloy in a mixture of approximately 10 m1. of concentrated hydrochloric acid and 2.5 ml. of concentrated nitric acid for each gram of sample, next adding approximately 7.5 drops of hydrofluoric acid per gram of sample to volatilize the silicon as a fluoride of silicon, then adding approximately ml. of 60% perchloric acid per gram of sample to the resulting silicon-free solution, heating the solution in a vessel to evaporate it to dense fumes of perchloric acid, continuing the heating until perchloric acid condenses down the sides of the vessel, cooling the solution, adding water, and boiling the solution to expel free chlorine, whereupon the presence of columbium in amounts of .02% and over is revealed by the presence of a turbid cloud of columbium oxide in the solution and then adding approximately ml. of boiling water per gram of sample, 25 m1. of concentrated sulphurous acid and 5 ml. of concentrated hydrochloric acid to the solution, then adding cellulose filtration accelerator to the solution, boiling the solution for a period on the order of five minutes and digesting the solution under heat until the solution is clear, then filtering the solution, washing the precipitate with hot dilute hydrochloric acid, heating the filter paper, filtration accelerator, and precipitate in an incinerator, to char the filter paper and filtration accelerator, and finally igniting the precipitated columbium oxide.

JAMES W. HlLLIARD.

REFERENCES CITED The following references are of record in the file of this patent:

A. S. T. M. Methods of Chemical Analysis of Metals; 1943; pp. '79 and 80.

Silverman, Journal of Industrial and Engineering Chemistry; Analytical Edition, vol. 6, page 287.

Cunningham, Journal of Industrial and Engineering Chemistry; Analytical Edition, vol. 10, pp. 233-235. 

